Answers: Multiple causes.
The discounting principle argues that when people can see that there might be several reasons for a person's behaviour, they tend to discount, or minimize, the importance of each reason, since they cannot be sure of which is the right one.
In this case, the people who watch the videotape cannot be sure of the soldiers intentions (i. e. whether the views expressed are truly his beliefs, or whether he was forced to say them because of his situation), so they will be inclined to discount them.
